DE602004001790T2 - Copper foil for chip-on-film use - Google Patents

Description

BACKGROUND OF THE INVENTION

1. Field of the invention

The This invention relates to a copper foil suitable for chip-on-film (COF) mounting in finely structured printed circuit boards is particularly suitable.

2. Description of the state of the technique

accompanying with the size reduction and weight loss of electronic devices are current electronic Integrated devices at an advanced level. Accordingly, it was It also required the density of circuit structures in the Increase printed circuit boards. Circuit structures are now formed with thin line widths and interconnect distances. Particular progress has been made with regard to increasing Density of IC mounting boards for driving liquid crystal displays and from PCs, mobile phones and PDAs. The ICs become instant Mounted on the board layer, what as a "chip-on-film" - (COF) Mount referred to as.

at The COF assembly is through the layer, which is connected to the connecting structures the copper foil is formed, passing light for detection used the IC positions. However, the visibility is more conventional Electrode-deposited copper foils used for printed circuit boards (Ability the detection of IC positions via Light), extremely poor. This is because of the big one surface roughness the copper foil. The light transmitting parts of the layer represent those parts in which the parts of the Kupferschaltkreisteilen different, not needed Etched copper foil has been. The detached ones Structures of the surface of the copper foil are applied to the layer surface when bonding the copper foil transferred to the layer and stay there. If light passes through the layer, so the amount of light passing in a straight line is due to the detached one Structures on the layer surface less and thus the visibility decreases.

There the visibility in conventional Electrode-deposited copper foils is weak for printed circuit boards, Two-layer materials are used, which consist of a polyimide layer exist on which a copper layer formed by sputtering becomes (thin film process), followed by plating with copper.

however is the adhesive strength this sputtered copper layer on the film weak and the etching solution or plating is in the formation of the circuit between the copper foil and erode the film, what the so-called "undercut" phenomenon leads. Because the adhesive strength Moreover, there is a risk that the copper layer while replaces the use of the product.

on the other hand was used as a method of treating the copper foil for a printed circuit board the process of roughening the surface of the copper foil by electroplating the same with a copper-cobalt-nickel alloy of copper and small amounts of cobalt and nickel are proposed (eg JP 2-292894). The By this roughening achievable copper foil is in terms of etchability, Alkaline grainability and resilience across from hydrochloric acid outstanding, however, several weak points were found such as a decrease in heat-resistant peel strength when using an acrylic-based Adhesive, insufficient oxidation resistance and a not blackening, but brown to charcoal brown Expected color (eg JP 9-87889). So far, no practical Achieved applications.

Thus, research has been driven to improve the copper foil. Methods for forming three-layer structures have been proposed which require plating the surface of a copper foil with an alloy of copper, wherein an amount of cobalt is about 1/10 that of copper and an amount of nickel is about 1/40 that of copper, followed by forming a cobalt-nickel alloy electroplated layer over it, followed by forming a zinc plating layer (e.g., JP 9-87888) or forming a zinc-nickel plating layer (e.g., JP 9-87889). Also, methods for forming three-layer structures which require roughening the surface of a copper foil by plating a copper alloy have been described, wherein an amount of cobalt is about 1/10 that of copper and an amount of nickel about 1/40 of that of copper. followed by forming a galvanic cobalt layer, after which a galvanic zinc layer (eg JP 8-335775) or a galvanic zinc-nickel layer (eg JP 8-335776) are additionally formed. These methods have been proposed in particular as a method for treating a copper foil, to reduce the decrease in adhesive strength between a copper foil and a resin substrate, which occurs due to the significantly higher temperature in the processing of printed circuit board manufacturing, along with the smaller size and higher integration of semiconductor devices and the heat generated during use of the devices Resistance to peeling on heating is further improved.

If however, the above improved copper foil having three-layer structure is included When COF mounting is used, the following problems occur.

The above copper foil is used to make a printed circuit board, which thinner the requirements Structures and mounted on the PCB ICs, where however, a mounting of the ICs on the circuit board a placement of solder balls on the circuits of the copper foil on the circuit board requires. To place solder balls on the copper foil is the adhesion with solder by galvanizing the copper foil with tin increases. The Tin-plating solution dissolves in this tin-galvano process the on the surface the copper foil particles present and leads to a significant impairment the peel strength between the copper foil and the circuit board.

A more copper foil for Printed circuit boards are known from EP-A-0 396 056.

OVERVIEW OF THE INVENTION

A The object of the invention is the specification of a copper foil, the a high etching factor has a formation of fine structures possible, in terms of the linearity lower lines of printed circuit boards and no particles which leaves the circuit patterns in the resin forming copper foil, no Waste of adhesive strength between the copper foil and the resin substrate while the formation of solder balls, excellent visibility shows and is also excellent in the assembly of ICs behaves fine structures.

to solution above object is given to a copper foil, which is a copper foil contains on which on at least one surface a layer of alloy particles provided with excellent roughness, the alloy particles form a copper-cobalt-nickel alloy whose content of cobalt and Nickel in each case the same size or is larger as their content of copper.

The Layer of alloy particles with excellent roughness, the on the surface the copper foil is provided may have a Stainproof treatment.

moreover For example, the layer of alloy particles having excellent roughness, the on the surface the copper foil is provided, a Silanhaftvermittler treatment exhibit.

By Treat the surface the layer of alloy particles with excellent roughness, the on the surface the copper foil is provided with a Stainproof treatment or a silane coupling agent treatment will it be possible an oxidation and discoloration to prevent the copper foil.

DESCRIPTION THE PREFERRED EMBODIMENTS

preferred embodiments a chip-on-film (COF) copper foil (hereinafter referred to as "COF foil") according to the invention are described in detail below.

The COF film of this embodiment consists of a copper foil, which on at least one surface a Has a layer of alloy particles with excellent roughness, wherein the alloy particles form a copper-cobalt alloy, their content of cobalt and nickel is equal to or greater than their content Copper.

The composition of the galvanized alloy of the layer of alloy particles having excellent roughness according to the invention overcomes the concept of the conventional composition of the galvanized alloy with small amounts of addition of both cobalt and nickel with respect to the copper and the concomitant consequence of not always satisfactory COF foil. The inventors have made various experiments without any limitations on the amounts of cobalt and nickel with respect to the copper. Here, the inventors have found that by increasing the amounts of addition of both cobalt and nickel in view of conventionally conceivable amounts Copper can be achieved as a COF film suitable copper foil. The inventors made further experiments and research, and thereby obtained a copper foil having a high etching factor, the possibility of forming fine structures, excellent linearity of lower lines of the circuit patterns without leaving particles of a copper foil forming the circuit patterns in the resin, and excellent visibility at least the side of the copper foil to be bonded to a resin substrate is provided with a layer of alloy particles excellent in roughness consisting of a copper-cobalt-nickel alloy and their content of cobalt and nickel is equal to or greater than their content of copper and in particular at this time, the composition of the deposited layer of alloy particles having excellent roughness per dm ² copper foil was 5 to 12 mg / dm ² copper, 6 to 13 mg / dm ² cobalt and 5 to 12 mg / dm ² nickel ,

moreover becomes the copper foil, on whose surface the particles with excellent Roughness deposited on a polyimide resin substrate and etched to form circuits, and the resulting COF (substrate) is over ICs placed while they can remain visible and the copper foil becomes when connecting the copper foil circuits and electroplated ICs with tin. If the temperature of the tin plating solution is in exceptionally high for this tin electroplating process, erodes the plating solution between the copper foil and the resin substrate, so that the undercut phenomenon occurs. In such applications, the composition is alloy particles fine roughness so formed that undercut does not occur.

The inventors have also studied this point of view and studied alloy compositions of particles having excellent roughness in which the undercut phenomenon does not occur, and through these investigations found out that the undercut phenomenon is adjusted to 1.2 to 2.2 mg / dm ² by adjusting the amount of cobalt mg / dm ^{2 of} copper and the amount of nickel can be suppressed to 1.0 to 2.0 mg / dm ² and that the undercut phenomenon by adjusting the amount of cobalt to 1.5 to 1.9 mg / dm ² per mg / dm ^{2 of} copper present and the amount of nickel can be reliably prevented to be 1.3 to 1.7 mg / dm ² , so that no decrease in the adhesive strength between the copper foil and the resin substrate due to the processing for forming solder balls is caused.

In particular, the deposition amount of the layer of alloy particles excellent in roughness on the copper foil surface should be in the range of 5 to 12 mg / dm ^{2 of} copper, 6 to 13 mg / dm ^{2 of} cobalt and 5 to 12 mg / dm ^{2 of} nickel. The reason for setting this range is mainly based on the results of the following experiment:

1st separation amount of copper

Below 5 mg / dm ² , the solubility in the etching solution becomes weak and etch residues are formed, while above 12 mg / dm ^2, the thermal resistance becomes poor.

2. Separation amount of cobalt

Below 6 mg / dm ² , the solubility in the etching solution becomes weak and etch residues are formed, and above 13 mg / dm ^2, the undercut phenomenon can not be reliably prevented.

3. separation quantity of nickel

Below 5 mg / dm ² , the undercut phenomenon can not be reliably prevented, whereas above 12 mg / dm ² the solubility in the etching solution becomes poor and etching residues form.

Examples 1 to 3

As the copper foil, an electrodeposited copper foil (B-WS foil manufactured by Furukawa Circuit Foil) was used. This was provided on its surface with a layer of alloy particles having excellent roughness by plating with a copper-cobalt-nickel alloy. The composition of the plating solution and the conditions of plating were as follows: Cu: 2 g / liter Co: 8 g / liter Ni: 8 g / liter Ammonium sulphate: 40 g / liter boric acid: 20 g / liter pH: 3.5 Temperature: 40 ° C Current density: 15 A / dm ²

The inventors have changed the plating duration under the above conditions to obtain various alloy compositions on the surfaces of the COF copper foil. The results obtained from this are shown in Table 1. Table 1 shows the contents of copper, cobalt and nickel, each in units of mg / dm ² . The relationships with respect to copper as 1 are shown in parentheses.

Table 1

Example 4

As a copper foil, a rolled copper foil (manufactured by Nippon Foil Manufacturing Co., Ltd.) was used. It was formed on its surface with a layer of alloy particles excellent in roughness by plating a copper-cobalt-nickel alloy. The composition of the plating solution and the electroplating conditions were as follows: Cu: 2 g / liter Co: 8 g / liter Ni: 8 g / liter Ammonium sulphate: 40 g / liter boric acid: 20 g / liter pH: 3.5 Temperature: 40 ° C Current density: 15 A / dm ²

The composition of the alloy on the surface of the COF copper foil produced under the above conditions is shown in Table 2. The inventors were able to achieve a copper foil with a smooth surface with Rz: 0.50 and Ra: 0.06. Table 2 shows the contents of copper, cobalt and nickel in units of mg / dm ² , respectively. The ratios to copper as 1 are shown in parentheses.

Table 2

The inventors bonded a polyimide film of a film producer A at a high temperature and high pressure to the surface of the copper foil which had been treated to deposit particles having excellent roughness in Examples 1 to 4, whereupon they were found to have excellent adhesiveness, ie, bondability. Now, the inventors have bonded a dry etching paint film on the surface of the copper foil and performed etching to provide a resin substrate for COF. In manufacturing this resin substrate for COF, the circuits were not corrugated, their linearity was extremely good, and a resin substrate for COF having excellent thin structures could be completed. This resin substrate could be positioned on a substrate with an IC placed thereon with a view of the ICs, and the position of the ICs could be easily confirmed from above the film and the ICs and circuits of the resin substrate could be precisely connected.

following The inventors included a polyimide film of a film manufacturer B. high temperature and high pressure on the surface of the deposit Particles with excellent roughness treated copper foil Examples 1 to 4 bonded, whereupon this excellent adhesiveness have stated. Then they have a dry etching paint film on the surface the copper foil bonded and an etch to provide a Resin substrates for COF performed. In making this resin substrate for COF, the circuits became not wavy, their linearity was extraordinary good and it could be a resin substrate for COF with excellent thin structures to get finished. This resin substrate could on a substrate with an IC placed on top of it, looking at the ICs be, with the position of the ICs in a simple way from above of the film confirmed and precisely connected the ICs and circuits of the resin substrate could become.

The Polyimide resin for bonding with the copper foil is slightly different in color or adhesion to the copper foil or other of the Manufacturer dependent Performance features, but the copper foils of the examples 1 to 4 when bonding with polyimide films of all manufacturers yielding results, after which they were made available the circuits etched and then in terms of visibility to confirm the IC position, adhesive strength, etc. were measured.

With treating the surface the layer of alloy particles with excellent roughness in the With regard to chromium rust prevention and silane coupling the obtained in Examples 1 and 2 copper foil and measuring the Visibility and adhesion etc. could be confirmed that the properties were satisfactory.

Holds to summarize the effects of the invention as explained above, so allows this one copper foil with a high etching factor, a formation of fine Structures with excellent linearity of lower lines of the circuit structures without leaving behind of particles forming the circuit structures in the resin Copper foil, avoiding a decrease in the adhesion between the copper foil and the resin substrate in the formation of solder balls, Excellent visibility and excellent installation of ICs on thin Structures.

Even though the invention with reference to the illustrative specific embodiments explained has to be taken into account, That a professional can perform many modifications, without to deviate from the scope of the invention, which is defined by the appended claims is.

Claims (3)

Copper foil for Chip-on-film use with a copper foil on at least a surface a layer of alloy particles with excellent roughness wherein the alloy particles are a copper-cobalt-nickel Alloy alloy whose content of cobalt and nickel are the same big or is larger as their content of copper. Copper foil for A chip-on-film use according to claim 1, wherein the on the copper foil provided layer of alloy particles with excellent Roughness has a Stainproof treatment. Copper foil for A chip-on-film use according to claim 1, wherein the on the copper foil provided layer of alloy particles with excellent Roughness has a Silanhaftvermittler treatment.